Model evaluation of denitrification under rapid infiltration basin systems

Area of Science:

• Environmental Engineering
• Water Resource Management
• Soil Science

Background:

• Rapid Infiltration Basin Systems (RIBS) are crucial for treating reclaimed wastewater and recharging groundwater.
• Denitrification (DNF) is the primary nitrogen removal process in nitrified effluent from sequenced batch reactors.
• Complex flow patterns in RIBS can significantly impact DNF efficiency.

Purpose of the Study:

• To characterize the effects of non-uniform flooding on denitrification in RIBS.
• To compare DNF predictions between coupled overland-vadose zone models and conventional flux boundary conditions.
• To identify operational parameters influencing nitrogen removal in RIBS.

Main Methods:

• A coupled overland flow-vadose zone model was implemented using the TOUGHREACT simulator.
• Simulations were conducted for two soil types under varying application cycles, hydraulic loading rates, wastewater quality, water table depths, and subsurface heterogeneity.
• Denitrification was simulated by varying key operational and environmental factors.

Main Results:

• Coupled flow models significantly improved DNF predictions compared to specified flux models, under-predicting by up to 450% in sand.
• Increased hydraulic loading rates and reduced wetting/drying ratios enhanced DNF by promoting anoxic conditions and faster water transport.
• Simulated DNF varied widely (2-49%) based on operational procedures and subsurface conditions, aligning with field observations.

Conclusions:

• Accurate DNF prediction in RIBS necessitates simulating coupled overland and vadose zone flow.
• Optimizing application cycles and hydraulic loading rates can enhance nitrogen removal.
• Understanding these factors is key to improving NO₃ removal in RIBS and ensuring effective wastewater treatment.